A bipartisan group of senators, including some of the GOP's foreign policy hawks, are encouraging President Barack Obama to explore diplomacy with Iran.

They caution, however, that actions will speak louder than words when it comes to the Iranian nuclear program.

"We support your efforts to explore a diplomatic opening, but we believe that the true test of Iranian sincerity is a willingness to match rhetoric with actions," the 10 senators, led by Foreign Relations Chairman Robert Menendez, D-N.J., wrote in a letter to Obama.

Signatories on Friday's letter include four Republicans: Lindsey Graham of South Carolina, John McCain of Arizona, Kelly Ayotte of New Hampshire and Roy Blunt of Missouri.

The letter comes in advance of P5 + 1 talks in Geneva intended to help bring about a diplomatic resolution to the threat of an Iranian nuclear weapons capability.

"The intent of sanctions is to force Iran to halt and dismantle its nuclear weapons program. Once this goal has been accomplished in a real, transparent, and verifiable way we will be prepared to remove existing sanctions in a measured, sequenced manner," the senators wrote. "However, at this time, we reaffirm that a credible military threat remains on the table and we underscore the imperative that the current sanctions be maintained aggressively, and call on you to increase pressure through sanctions already in place."

The full letter appears below:

As representatives of the P5+1 and the Iranian government prepare to enter another round of negotiations to verifiably end Iran’s nuclear weapon program, we reiterate the four strategic elements articulated by 76 Senators to you on August 2, 2013 necessary to achieve resolution of the nuclear issue: (1) an explicit and continuing message that we will not allow Iran to acquire a nuclear weapons capability, (2) a sincere demonstration of openness to negotiations by Iran, (3) the maintenance and toughening of sanctions, and (4) a convincing threat of the use of force.

We support your efforts to explore a diplomatic opening, but we believe that the true test of Iranian sincerity is a willingness to match rhetoric with actions. The critical test will be Iran’s proposal to the P5+1 this week in Geneva. Iran’s first confidence-building action should be full cooperation with the International Atomic Energy Agency, fulfillment of its responsibilities under the Nuclear Nonproliferation Treaty, and implementation of all Resolutions passed by the United Nations Security Council regarding Iran’s nuclear weapons program, to include immediate suspension of all enrichment activity. If the Iranian government takes these steps in a verifiable and transparent manner, we are willing to match Iran’s good-faith actions by suspending the implementation of the next round of sanctions currently under consideration by the Congress. In short, the U.S. should consider, with the other members of the P5+1, a “suspension for suspension” initial agreement - in which Iran suspends enrichment and the U.S. suspends the implementation of new sanctions.

For the P5+1 states, such an agreement would ease concerns that Iran is using the talks as a subterfuge while its centrifuges spin and for Iran it would suspend critical additional sanctions on its key economic sectors.

The intent of sanctions is to force Iran to halt and dismantle its nuclear weapons program. Once this goal has been accomplished in a real, transparent, and verifiable way we will be prepared to remove existing sanctions in a measured, sequenced manner. However, at this time, we reaffirm that a credible military threat remains on the table and we underscore the imperative that the current sanctions be maintained aggressively, and call on you to increase pressure through sanctions already in place.

A nuclear weapons capable Iran threatens regional stability and international security and directly threatens U.S. national security interests. As we previously cautioned, Iran has historically used negotiations to affect progress on its nuclear weapons program. We must continue to realistically evaluate Iranian intentions, and we reiterate that the centrifuges cannot be allowed to continue spinning.

We reject Iranian statements that Iran should be able to continue enrichment in its own territory. Indeed, this is not a prerequisite for a peaceful nuclear energy program. Countries from Canada, to Mexico and South Africa benefit from peaceful nuclear energy programs, without indigenous enrichment programs. Iran does have a right to a peaceful nuclear energy program; it does not have a right to enrichment.

We remind you that the U.S. Department of State has characterized Iran as “the most active state sponsor of terrorism” and to be sure, verifiable dismantlement of the Iranian nuclear weapons program will not resolve the Iranian government’s deplorable abuse of basic human rights, denial of basic civil freedoms, or its ongoing activities that seek to destabilize the region.

We remain hopeful that talks next week in Geneva lead to concrete Iranian actions to prove to the world that Iran does not seek a nuclear weapons capability. However, if Iranian actions fail to match the rhetorical reassurances of the last two weeks, we are prepared to move forward with new sanctions to increase pressure on the government in Tehran.